1. Field of the Invention
The present invention relates to an electromagnetic wave information detection apparatus and an electromagnetic wave information detection method, and more particularly, to an indirect conversion type radiation imaging apparatus and a method which obtain an image by converting radiation into visible light.
2. Related Art
J. Non-Cry. Sol. 299-302 (2002) 1240-1244 discloses an indirect conversion type imaging element that uses a scintillator (GOS: gadolinium oxysulfide) which converts radiation into visible light, and an organic photoelectric conversion film (OPC) which serves as a photoelectric conversion film converting visible light into an electrical signal and is a laminate of a charge generation layer (benzimidazole) and a hole transport layer (polycarbonate and TPD (N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine)). However, the literature does not disclose anything about the presence or absence of an afterimage generation or an elimination method of the afterimage when such an imaging element is used.
U.S. Pat. No. 6,171,643 discloses a direct conversion type radiation imaging element that does not use a scintillator but uses a multi-layer structure containing amorphous selenium and a method of driving the radiation imaging element. The multi-layer structure has a p-layer (As2Se3 layer), an i-layer (amorphous selenium thick layer), and an n-layer (amorphous selenium layer with doped alkali metal). Sensitivity may be stabilized by short-circuiting between upper and lower electrodes for a short period of time to neutralize space charges in a detector after an X-ray irradiation. This advantage is achieved by a layer (As2Se3 layer) with lower resistance than that of an amorphous selenium layer that performs generating charges and transporting the charges. Thus, it is considered that the As2Se3 layer is essential, and the advantage is said to be achieved because the As2Se3 layer has low resistance since the As2Se3 layer has more free holes than the amorphous selenium layer. A junction between the As2Se3 layer and a substrate electrode is said to perform the role of “charge injection”, thereby accelerating the neutralization of negative space charges. However, the As2Se3 layer has problems in that, for example, it has low heat resistance, evaporation cost is high, and toxicity is significant. U.S. Pat. No. 6,171,643 relates to a direct conversion type radiation imaging element that does not use scintillator but uses amorphous selenium, and does not disclose either the presence or absence of an afterimage generation in an imaging element including a photoelectric conversion film having a charge generation layer and a charge transport layer nor an elimination method of the afterimage.
The present inventors have found that sensitivity varies in an imaging element including a photoelectric conversion film having a charge generation layer and a charge transport layer when the imaging element continuously captures images in many times or the imaging element captures an image with a large dosage.